This invention relates to a low density, closed cell foamed thermoplastic multi-block copolymer elastomer for use as midsoles for athletic shoes.
Midsoles for athletic shoes have been characterized as the most important part of footwear. This portion of the shoe is the interface between the foot of the wearer and the ground. The rather significant force at which the foot of a runner strikes the ground, especially at the toe and heel portions, is transmitted through the body of runner. The force developed is absorbed in significant part by the midsole of the shoe. The midsole returns the impact energy to the body and creates in the runner a beneficial sensation of springiness. Energy return ratios generated by currently used midsoles in athletic shoes are deficient. Also, usually the midsoles of athletic running shoes lose their weight bearing capacity after about two hundred fifty-miles of use. This is due to the large number of compression and return cycles that the midsole is subjected to which results in a considerable reduction in cushioning effect. A need in the industry exists for a low density, foamed polymer that exhibits excellent shock attenuation characteristics and that has the property of storing elastic energy in the midsole and returning a substantial portion of that energy, i.e., energy return, which gives the runner a sensation of springiness. Also, there is need for midsoles in athletic shoes that do not break down after extended use due to loss of weight bearing capacity, i.e., fatigue, thus shortening the useful life of the shoe.